Aspiration into the airways is one of the major causes of lung disease in infants and young children. Unfortunately the diagnosis of aspiration is often delayed due to unawareness and to the low sensitivity and specificity of existing diagnostic tests.
Aspiration of food or gastric material into the tracheobronchial tree can result in a variety of disease states such as laryngeal and tracheo-bronchial inflammation leading to stridor, cough, wheezing, recurrent pneumonia, bronchiectasis, pulmonary fibrosis and even suffocation and death due to massive aspiration (Mendelson C L. The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol 1946; 52: 191-205; Bauer M L, Figueroa-Colon, Georgeson K, Young D W. Chronic pulmonary aspiration in children. South Med J 1993; 86: 789-795; Moran T J. Experimental aspiration pneumonia. Arch Pathol 1955; 60: 122-129).
The common conditions that predispose to aspiration in infants and young children include prematurity due to developmental delay of the coordination between swallowing and breathing (Harding R. Johnson P, McClealand M E. Liquid sensitive laryngeal receptors in the developing ship cat and monkey. J Physiol Lond 1978; 277: 409-422), abnormal communication between airways and esophagus such as laryngo-tracheal cleft or tracheo-esophageal fistula, massive gastro-esophageal reflux, and neurological abnormalities such as cerebral palsy, vocal cord paralysis and familial dysautonomia.
The available tests for the diagnosis of aspiration such as barium swallow during videofluoroscopy and gastroesophageal scintigraphy are not sensitive enough (McVeagh P. Howman-Giles R, Kemp A. Pulmonary aspiration studied by radionuclide milk scanning and barium swallow roentgenography. Am J Dis Child 1987; 141: 917-921). In 1985, Corwin and Irwin (Corwin R W, Irwin R S. The lipid-laden alveolar macrophage as a marker of aspiration in parenchymal lung disease. Am Rev Respir Dis 1985; 132: 576-581) introduced the Oil-Red-O staining of lipid laden alveolar macrophages (LLAM) as a marker for aspiration. More recently, others have noticed that this test is not specific for aspiration and that other conditions can also result in an increase in fat vacuoles inside alveolar macrophages (Kajetanowicz A, Stinson D, Laybolt K S, Resch L. Lipid-laden macrophages in tracheal aspirate of ventilated neonates receiving intralipid. Pediatr Pulmonol 1999; 28: 101-108; Knauer-Fisher S, Ratjen F. Lipid-laden macrophages in bronchoalveolar lavage fluid as a marker for pulmonary aspiration. Pediatr Pulmonol 1999; 27: 419-422; Vichinsky E, Williams R, Das M, Earles A N, Lewis N, Adler A, McQuintty J. Pulmonary fat embolism: a distinct cause of severe acute chest syndrome in sickle cell anemia. Blood 1994; 11: 3107-3122).
Elidemir and his colleagues (Elidemir O, Fan L L, Colasurdo N. A novel diagnostic method for pulmonary aspiration in a murine model. Immunocytochemical staining of milk proteins in alveolar macrophages. Am J Respir Crit Care Med 2000; 161: 622-626) have recently shown that aspiration of milk in mice could be diagnosed by specific immunocytochemical staining of milk proteins in bronchoalveolar macrophages. Although this method seems to be specific for the detection of milk, aspiration of other food substances cannot be detected by this method. Furthermore they stained milk proteins (α-lactalbumin and β-lactoglobulin) in alveolar macrophages by an immunocytochemical method. They found that their method is very sensitive and very specific as compared to Oil-Red O staining, but the stainings were positive only for the 3-4 days following induced aspiration. Aspiration can occur from above as in children with neurologic impairment, but may be secondary to gastro-esophageal reflux and may occur only during the massive episodes and not necessarily every day.